Is Arthrosamid worth considering for my knee osteoarthritis?

Arthrosamid is most often considered at the point where knee osteoarthritis symptoms are starting to limit day-to-day life (for example, pain on stairs or walking), but non-surgical care has not been enough. In UK practice it tends to sit between “simpler” injections and surgery: a single, ultrasound-guided injection into the knee joint intended to reduce pain and improve function, rather than cure arthritis or regrow cartilage. It is positioned by UK hospital information for mild-to-moderate degenerative knee osteoarthritis, and it is not used for inflammatory arthritis (such as rheumatoid arthritis) or for severe “bone-on-bone” disease where knee replacement is usually the more effective option.

What makes Arthrosamid different from steroid or hyaluronic acid injections is the material itself: it is a non-biodegradable (permanent) synthetic hydrogel placed within the joint lining (synovial membrane), rather than a drug intended to wear off over weeks. The aim is longer-lasting cushioning and friction reduction inside the knee; in practice, that means it is typically discussed by clinicians when a longer-acting, one-off option is being weighed against repeated injections or progressing towards an operation.

The evidence so far is encouraging but still developing. In a multi-centre open-label study of 49 people (mean age 70) with symptomatic and radiographic knee osteoarthritis who received a single 6 ml ultrasound-guided polyacrylamide hydrogel injection, average WOMAC pain improved by 17.7 points on a 0–100 scale at 52 weeks, and 62.2% met OMERACT–OARSI responder criteria at one year; no new adverse events between weeks 26 and 52 were considered device-related. Beyond that, an observational “real-world” study (LUNA) reported early 2025 results in 199 participants with moderate-to-severe knee osteoarthritis, with pain relief described as sustained up to 12 months and planned follow-up for up to five years. Separately, an NHS Health Research Authority (HRA) research summary notes prior datasets suggesting benefits lasting beyond two years for the majority, while also indicating that detailed independent long-term data remain limited.

From a regulatory point of view, Arthrosamid received a European CE mark in 2021 for symptomatic treatment of knee osteoarthritis—approval focused on symptom relief and safety, not disease modification. In the UK, the HRA also notes that steroid injections are the only intra-articular injection routinely available within standard NHS care at present, which helps explain why Arthrosamid is often accessed privately or within research settings. The next step in deciding where it fits is usually clarifying whether the pattern and severity of osteoarthritis match the “mild-to-moderate, non-inflammatory” group most often offered it, and how it compares in practice with other injection options for the same stage of knee OA.

Who tends to benefit most and who might not?

In UK clinic information, Arthrosamid is generally framed for adults whose knee symptoms fit degenerative osteoarthritis and whose imaging (X‑ray, ultrasound or MRI) still shows some usable joint space rather than complete “bone‑on‑bone” collapse. In practical terms, this often means people who can still walk and manage day-to-day tasks, but pain becomes the limiting factor after a predictable amount of loading (for example, after 20–30 minutes of walking, on stairs, or when getting up from a chair), despite a period of non-surgical care. A specialist assessment is still needed to confirm that the pain pattern matches osteoarthritis and that the joint is at a stage where an injection has a realistic chance of helping.

Arthrosamid is also usually discussed after the “core” options have been tried without enough relief: a targeted exercise or physiotherapy programme, weight optimisation where relevant, and simple painkillers. UK hospital guidance places it in the mild-to-moderate degenerative knee OA group rather than as a first-line treatment, and it is explicitly not aimed at inflammatory arthritis (for example rheumatoid arthritis) or very advanced end-stage OA where knee replacement is often considered the more effective pathway. The same “not for inflammatory / not for bone‑on‑bone” boundary is one of the quickest ways clinicians triage who is less likely to benefit.

Quick self-check: green flags and yellow flags

• Green flags (more typical fit): radiographic knee osteoarthritis; persistent pain and stiffness affecting function; symptoms continue despite physiotherapy/exercise and other non-surgical measures; imaging suggests the knee is not end-stage “bone-on-bone”. (This is the group described as “mild-to-moderate” degenerative OA in UK hospital information.)
• Yellow flags (may be less suitable or need a different plan): inflammatory arthritis diagnoses (for example rheumatoid arthritis); severe “bone‑on‑bone” osteoarthritis where joint replacement is usually discussed; situations where imaging and symptoms do not line up clearly enough to make an intra‑articular hydrogel injection a sensible next step.

Published outcomes also help set expectations about who benefits. In a 52‑week (12‑month) open-label study of 49 people (mean age 70) given a single 6 ml ultrasound-guided polyacrylamide hydrogel injection, average WOMAC pain improved by 17.7 points on a 0–100 scale at 52 weeks, and 62.2% met OMERACT–OARSI responder criteria at one year. Put plainly, that is “around six in ten” meeting a standard definition of meaningful improvement—so a substantial minority did not get a major response even in a carefully selected study population.

Some UK clinics describe results more simply as a “more than 70%” success rate (usually meaning meaningful pain reduction and improved mobility in most treated patients). That kind of headline figure can be a helpful shorthand, but it still leaves room for non-responders, and it may not apply equally across different severities of osteoarthritis. Across both research reporting (for example, the 62.2% responder rate at 12 months) and clinic-style reporting (>70% success), the recurring theme is variability: response can differ with osteoarthritis severity, overall health, activity demands, and individual biology—so selection based on imaging and clinical assessment remains central.

What actually happens during an Arthrosamid injection?

A typical Arthrosamid appointment is designed as a single outpatient visit, with the “work” done by image-guided placement rather than anything like an operation. In UK research and hospital descriptions, the aim is to put a soft synthetic hydrogel into the knee joint so it can settle into the joint lining (the synovial membrane) and act as a cushioning, shock‑absorbing layer that may reduce friction, pain and inflammation over time.

Before the injection: confirming it is the right knee problem

The first step is usually a clinical review alongside imaging (commonly X‑ray and sometimes ultrasound or MRI) to confirm osteoarthritis and check severity. In the NHS HRA-described study set-up, baseline symptoms are recorded using measures such as a pain visual analogue scale (VAS) and questionnaires including KOOS and WOMAC, with planned reviews at 3, 6 and 12 months—a useful guide to the sort of follow-up schedule many services consider appropriate.

On the day: what the procedure is like

UK hospital protocols describe practical steps to lower risk and improve accuracy. Benenden Hospital, for example, describes giving a single oral antibiotic dose 1–2 hours before the injection and using local anaesthetic so the skin and deeper tissues are numbed. The needle is then placed into the joint using ultrasound guidance, and the gel is injected into the synovial cavity; in the HRA research summary, synovial fluid aspiration is also described as part of the sterile technique. The procedure is typically carried out in an ambulatory care unit or treatment room, and people are generally able to walk out the same day.

The “permanent gel” trade-off

Unlike steroid or hyaluronic acid injections, Arthrosamid is intended to be non‑biodegradable (not quickly absorbed). That permanence is part of why it is discussed as a potentially longer-acting, one‑off symptom option, but it also means that if a problem occurred, revision may be more complex than simply waiting for a drug to wear off. Published and public summaries commonly describe outcomes out to 12 months, with longer-term (>2 years) benefit suggested in some datasets, while detailed independent very-long-term follow-up remains more limited.

Aftercare and what tends to be “normal” in the first days

Short-term side effects described across UK hospital information and clinical reporting are usually local and temporary: a sore or aching knee, bruising, redness or swelling around the injection site, and sometimes a sense of fullness or tightness in the joint. These effects are commonly described as settling over days to a couple of weeks. In the 12‑month iPAAG study, there were no new device‑related complications reported between weeks 26 and 52, supporting a broadly reassuring one‑year safety picture in that small open-label cohort.

What does the evidence actually show so far?

Taken together, the published studies to date support one clear, repeatable takeaway: in small-to-moderate sized cohorts, a single Arthrosamid-class polyacrylamide hydrogel injection has been associated with meaningful symptom improvement for many people with knee osteoarthritis over about 12 months, but the confidence in “how much better it is than other options” remains limited because the strongest datasets are not randomised, blinded comparisons.

The most detailed 12‑month outcomes come from a multicentre open-label study of 49 people with symptomatic, radiographic knee osteoarthritis (mean age 70). Everyone received the same treatment (a single 6 ml, ultrasound-guided intra‑articular polyacrylamide hydrogel injection) and was followed to 52 weeks. On average, pain and function scores improved: WOMAC pain fell by 17.7 points (0–100 scale) at one year, and 62.2% met the OMERACT–OARSI definition of a “responder” (a standard threshold for meaningful improvement). Safety reporting in that paper did not identify new device-related problems between weeks 26 and 52.

What that study cannot do (by design) is separate the injection’s specific effect from other reasons symptoms can change over a year — including natural ups and downs, the placebo effect/expectations, or other care people continue alongside injections. Without a blinded comparison group (for example a sham injection, steroid or hyaluronic acid), it is not possible to put a precise number on the “extra” benefit attributable to the hydrogel itself.

Beyond that 49‑patient study, the largest publicly described dataset so far is the LUNA multicentre observational study, which enrolled 199 people with moderate-to-severe knee osteoarthritis who received a single 6 ml injection. Early results presented in 2025 reported sustained pain relief for many participants out to 12 months, with follow‑up planned for up to 5 years. As an unblinded, non‑randomised study sponsored by the manufacturer, it is helpful for real‑world signals and longer follow‑up, but it still cannot answer head‑to‑head questions such as “is it better than steroid in similar patients?”

For durability beyond a year, the NHS Health Research Authority (HRA) research summary notes that Arthrosamid has been shown to be safe and effective, with benefits lasting beyond two years in the majority of treated patients in prior datasets; however, detailed independent results beyond about 2–3 years are still relatively sparse in the public domain.

What would meaningfully reduce the uncertainty?

A large, blinded randomised trial showing that Arthrosamid provides clearly greater, longer-lasting improvement than a sham injection (and ideally also versus common comparators such as steroid or hyaluronic acid) at around 12–24 months, with a reassuring rate of serious adverse events, would materially strengthen confidence in its relative effectiveness and cost‑effectiveness.

How much does Arthrosamid cost in the UK?

In the UK, Arthrosamid is most often priced and delivered as a private self-pay option rather than a routine NHS injection. The NHS Health Research Authority (HRA) summary notes that, in standard NHS practice, steroid injections are the only intra‑articular injection routinely available for knee osteoarthritis, with Arthrosamid being evaluated in a specific study setting.

Across UK private providers, quoted prices for one knee commonly sit in a broad guide band of around £2,000–£3,000 per injection, depending on what is bundled into the package. Examples of publicly advertised figures show the upper end in central London: St John & St Elizabeth Hospital lists Arthrosamid packages starting from about £3,025 for one knee and around £5,895 for both knees. A Kent/London musculoskeletal clinic also quotes Arthrosamid as typically £2,100–£3,000 per injection.

A practical way to make sense of these ranges is to picture a “typical quote” as a bundle of components rather than a single line item. For example, a one‑knee package priced at ~£2,500 might include: an initial specialist assessment, diagnostic imaging (often an X‑ray, sometimes ultrasound or MRI), the Arthrosamid device cost, the ultrasound‑guided injection appointment, and at least one follow‑up review. In other clinics, some of those elements (most often imaging and follow‑up) may be charged separately, so two quotes with the same headline price are not always comparable.

Price differences are usually driven by a handful of predictable factors: location (London and other major cities are often higher), whether care is consultant‑led, the facility type (specialist orthopaedic centres versus more general clinics), and whether pricing is fully bundled or itemised across consultation, imaging and procedure.

When comparing quotes, it often helps to pin down three specifics in writing:

• Whether the price is per knee and whether it includes consultation + imaging (X‑ray/ultrasound/MRI).
• Whether follow‑up is included (for example, a review appointment) and what happens if symptoms do not improve.
• Whether any extras are expected (for example, additional imaging or appointments beyond the first review).

Relative to other injections, UK clinic pricing guides generally place steroid injections at the lower-cost end, with hyaluronic acid and platelet‑rich plasma (PRP) in the mid‑to‑higher range, and Arthrosamid often towards the higher end because of the device cost and the nature of the appointment.

Search MSK lists specialists across the UK who offer knee osteoarthritis injections, including Arthrosamid—filter by region and specialty to find local options and compare like‑for‑like quotes.

How do I choose a reputable Arthrosamid clinic and specialist?

Clinic quality tends to show up in two places: who is doing the injection and how often they manage knee osteoarthritis injections. UK hospital information describes Arthrosamid as being delivered by a consultant-led team using ultrasound guidance for intra‑articular placement, which is a useful benchmark when comparing providers (for example, Benenden Hospital’s pathway). A reputable service can usually state the clinician’s specialty (such as orthopaedics, sports and exercise medicine, or musculoskeletal imaging) and whether ultrasound‑guided joint injections are a routine part of their practice.

A thorough assessment is more than a quick “yes/no” to Arthrosamid. Good practice normally includes a structured history (pain pattern, swelling, locking/giving way), a focused knee examination, and a review of recent imaging (commonly X‑ray, sometimes ultrasound or MRI) to confirm that osteoarthritis is the main pain driver and to check whether other treatments may be more appropriate. Clear clinics also discuss the full menu of reasonable options—rehabilitation/physiotherapy, other injection types, and surgical pathways where relevant—rather than jumping straight from enquiry to procedure.

For procedural standards, Benenden Hospital’s published protocol offers a concrete reference point: the injection is performed in an ambulatory care setting under local anaesthetic, with ultrasound-guided needle placement into the synovial cavity and an infection‑risk strategy that includes an oral antibiotic 1–2 hours before the procedure. Sterile technique, image-guided accuracy, and an appropriate outpatient environment matter because Arthrosamid is intended to remain in the joint, so the “day-of” process is not just a formality.

Transparency is another strong trust marker. Reputable clinics tend to explain, in writing, what Arthrosamid is and what it is not, give a balanced summary of risks and alternatives, and set expectations that outcomes vary. For example, a UK musculoskeletal clinic FAQ cites a “more than 70%” success rate in studies while still emphasising that response can depend on factors such as osteoarthritis severity—an approach that is optimistic but not absolute.

Useful questions to bring to an initial appointment (or to ask on the phone) include:

• “Which clinician will do the injection, and what is their background in knee osteoarthritis and ultrasound‑guided intra‑articular injections?”
• “Which imaging will be reviewed (X‑ray/ultrasound/MRI), and how does it affect suitability and expected benefit?”
• “Will the injection be ultrasound-guided, and is it done under strict sterile conditions in an outpatient/ambulatory unit?”
• “What infection‑prevention steps are used (for example, any antibiotic protocol), and what are the clinic’s ‘what if’ plans if pain flares after injection?”
• “What follow‑up is included (for example, a review appointment), and what happens if there is little or no improvement?”
• “Is pricing fully itemised or packaged, and what exactly is included (consultation, imaging, procedure, follow‑up)?”

Rather than repeating the eligibility labels already used earlier, the practical decision frame here is whether the clinic can evidence (1) specialist assessment and imaging review, (2) high‑quality sterile, ultrasound‑guided delivery, and (3) transparent expectations and follow‑up. Search MSK can be used to find UK specialists who offer Arthrosamid and compare providers by region and specialty using these same checkpoints.